This invention is directed to an improved process for preparing polyarylates.
Polyarylates are polyesters derived from a dihydric phenol, particularly 2,2-bis(4-hydroxyphenyl)propane, also identified as Bisphenol-A, and an aromatic dicarboxylic acid, particularly mixtures of terephthalic and isophthalic acids. These polyarylates are high temperature, high performance thermoplastic polymers with a good combination of thermal and mechanical properties. They also have good processability which allows them to be molded into a variety of articles.
Many processes have been described in the literature for the preparation of polyarylates. One such process is the diacetate process. In the diacetate process, a dihydric phenol is converted to its diester derivative, which is then reacted with an aromatic dicarboxylic acid(s) to form the polyarylate.
However, the polyarylate produced by the diacetate process have a tendency to be colored which could make them unsuitable in some end use applications. Thus there is a desire to improve the color of the polyarylate for such end use applications.
Activated charcoal and other adsorbents have been used to remove color or odor from liquids and gases. (V. R. Deitz, Bibliography of Solid Adsorbents, Washington, D.C., 1944; J. M. Brown, Revere Sugar Refinery, Charleston, Mass.). For example, extremely large quantities of fuller's earth and other adsorbents are used in purifying petroleum products (C. L. Mantell, "Adsorption," McGraw Hill, New York, 1945). However, the use of adsorbents such as activated charcoal to remove color from polymers is not seen reported in the literature. This may be due to the relative ineffectiveness of removing color from high molecular weight polymers with adsorbents. The use of adsorbents during a polymerization reaction has not been seen to be reported in the literature. There are extensive literature references which show the chemical reactivity of charcoal and other adsorbents. (Zechmeister, McNeely, and Solyom, J. Am. Chem. Soc., 64, 1922 (1942). For example, some charcoals are known oxidizing agents at higher temperatures which would increase the color of most polymers. (E. Ledoux, "Vapor Adsorption, Industrial Applications and Competing Processes," Chemical Pub. Co., Brooklyn, 1945). In addition, physical adsorption decreases with increasing temperature. Thus, the use of adsorbents to improve the color of polyarylate is unexpected.